<!--歌曲（歌手，排行）详情页面的子组件的头部部分（名字和背景图）-->
<template>
  <div class="music-list">
    <div class="back" @click="back">
      <i class="icon-back"></i>
    </div>
    <h1 class="title" v-html="title"></h1>
    <div class="bg-image" :style="bgStyle" ref="bgImage">
      <!--播放全部的按钮-->
      <div class="play-wrapper">
        <div ref="playBtn" v-show="songs.length>0" class="play" @click="random"> <!--根据歌曲列表的长度显示按钮-->
          <i class="icon-play"></i>
          <span class="text">随机播放全部</span>
        </div>
      </div>
      <!--播放全部的按钮-->
      <div class="filter" ref="filter"></div> <!--高斯模糊的层-->
    </div>
    <div class="bg-layer" ref="layer"></div><!--随着歌单推动图片向上滚动层-->
    <scroll :data="songs" @scroll="scroll"
            :listen-scroll="listenScroll" :probe-type="probeType" class="list" ref="list">
      <div class="song-list-wrapper">
        <song-list :songs="songs" :rank="rank" @select="selectItem"></song-list>
       <!-- @select是子组件封装的点击事件-->
      </div>
      <div v-show="!songs.length" class="loading-container"> <!--如果歌曲列表的长度没有则显示加载状态-->
        <loading></loading>
      </div>
    </scroll>
  </div>
</template>

<script type="text/ecmascript-6">
  import Scroll from 'base/scroll/scroll'
  import Loading from 'base/loading/loading'
  import SongList from 'base/song-list/song-list' // 歌曲列表部分的组件引用
  import { prefixStyle } from 'common/js/dom'
  import { playlistMixin } from 'common/js/mixin'
  import { mapActions } from 'vuex'

  const RESERVED_HEIGHT = 40  // 预留滚动距离40（就是头部）
  const transform = prefixStyle('transform') // 适配的浏览器内核的
  const backdrop = prefixStyle('backdrop-filter')

  export default {
    mixins: [playlistMixin],
    props: {
      // 接收参数
      bgImage: { // 背景图
        type: String,
        default: ''
      },
      songs: {
        type: Array,
        default: []
      },
      title: {
        type: String,
        default: ''
      },
      rank: {
        type: Boolean,
        default: false
      }
    },
    data () {
      return {
        scrollY: 0  // 滚动的值
      }
    },
    computed: {
      bgStyle () { // 通过bind绑定的style通过计算属性获取背景图
        return `background-image:url(${this.bgImage})`
      }
    },
    created () {
      this.probeType = 3
      this.listenScroll = true // 监听滚动事件
    },
    mounted () { // 计算背景图的高度从而计算背景图底部的歌曲列表的高度
      this.imageHeight = this.$refs.bgImage.clientHeight // 背景图的高度
      this.minTransalteY = -this.imageHeight + RESERVED_HEIGHT // 最小的滚动值
      this.$refs.list.$el.style.top = `${this.imageHeight}px`
    },
    methods: {
      // mixin 里面的方法适配底部
      handlePlaylist (playlist) {
        const bottom = playlist.length > 0 ? '60px' : ''
        this.$refs.list.$el.style.bottom = bottom // $el和js里面的document.getElementBy..一样的道理
        this.$refs.list.refresh() // 因为是scroll组件所以在适配的时候要调用refresh[所以在子组件里也会有一个这样的方法，方便父组件使用]
      },
      scroll (pos) {
        this.scrollY = pos.y  // 取得scrollY的值，来计算bgImage的推动
      },
      back () {
        this.$router.back() // 返回上一个页面
      },
      // 点击歌曲列表时播放
      selectItem (item, index) {
        this.selectPlay({
          list: this.songs,
          index
        })
      },
      // 随机播放的按钮
      random () {
        this.randomPlay({
          list: this.songs
        })
      },
      ...mapActions([ // 调用vuex的actions的方法
        'selectPlay',
        'randomPlay'
      ])
    },
    watch: {
      scrollY (newVal) {
        let translateY = Math.max(this.minTransalteY, newVal)
        let scale = 1 // 设置背景图片的缩放
        let zIndex = 0
        let blur = 0 // 首先设置模糊值为0
        const percent = Math.abs(newVal / this.imageHeight) // 绝对值（背景图根据下拉实现图片放大）
        if (newVal > 0) {
          scale = 1 + percent
          zIndex = 10
        } else {
          blur = Math.min(20, percent * 20) // 设置图片的模糊最大值是20[列表往上推实现图片的模糊]
        }

        this.$refs.layer.style[transform] = `translate3d(0,${translateY}px,0)`
        this.$refs.filter.style[backdrop] = `blur(${blur}px)` // 高斯模糊只有iOS效果较好
        if (newVal < this.minTransalteY) { // 如果滚动到距离头部的最小距离就是距离头部40的时候
          zIndex = 10 // 让背景图的图层升高作为头部（overflow headed 的状态）
          this.$refs.bgImage.style.paddingTop = 0
          this.$refs.bgImage.style.height = `${RESERVED_HEIGHT}px`
          this.$refs.playBtn.style.display = 'none' // 如果列表滑动到头部的时候，按钮消失
        } else {
          this.$refs.bgImage.style.paddingTop = '70%'
          this.$refs.bgImage.style.height = 0
          this.$refs.playBtn.style.display = '' // 如果列表向下拉动，则按钮显示
        }
        this.$refs.bgImage.style[transform] = `scale(${scale})`
        this.$refs.bgImage.style.zIndex = zIndex
      }
    },
    components: {
      Scroll,
      Loading,
      SongList
    }
  }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"
  @import "~common/stylus/mixin"

  .music-list
    position: fixed
    z-index: 100
    top: 0
    left: 0
    bottom: 0
    right: 0
    background: $color-background
    .back
      position absolute
      top: 0
      left: 6px
      z-index: 50
      .icon-back
        display: block
        padding: 10px
        font-size: $font-size-large-x
        color: $color-theme
    .title
      position: absolute
      top: 0
      left: 10%
      z-index: 40
      width: 80%
      no-wrap()
      text-align: center
      line-height: 40px
      font-size: $font-size-large
      color: $color-text
    .bg-image
      position: relative
      width: 100%
      height: 0
      padding-top: 70%
      transform-origin: top
      background-size: cover
      .play-wrapper
        position: absolute
        bottom: 20px
        z-index: 50
        width: 100%
        .play
          box-sizing: border-box
          width: 135px
          padding: 7px 0
          margin: 0 auto
          text-align: center
          border: 1px solid $color-theme
          color: $color-theme
          border-radius: 100px
          font-size: 0
          .icon-play
            display: inline-block
            vertical-align: middle
            margin-right: 6px
            font-size: $font-size-medium-x
          .text
            display: inline-block
            vertical-align: middle
            font-size: $font-size-small
      .filter
        position: absolute
        top: 0
        left: 0
        width: 100%
        height: 100%
        background: rgba(7, 17, 27, 0.4)
    .bg-layer
      position: relative
      height: 100%
      background: $color-background
    .list
      position: fixed
      top: 0
      bottom: 0
      width: 100%
      background: $color-background
      .song-list-wrapper
        padding: 20px 30px
      .loading-container
        position: absolute
        width: 100%
        top: 50%
        transform: translateY(-50%)
</style>
